1. Technical Field
A process for forming ultra fine patterns using a bottom anti-reflective coating film containing an acid generator is disclosed. More specifically, a process for forming vertical patterns is disclosed that uses an organic bottom anti-reflective coating film containing excessive amount of an acid generator in order to prevent formation of sloping patterns due to the photoresist resins absorbing light of wavelength used as the light source, even when photoresist resins having a high absorbance to light source are utilized.
2. Description of the Related Art
A fine circuit of 150 nm L/S has been formed in a process of manufacturing semiconductor fine circuits using KrF of 248 nm, and an attempt has been recently made to form patterns of 150 nm or less. Further, a study on the process of manufacturing fine circuits using light sources having low wavelength such as ArF(193 nm), VUV(157 nm) and EUV(Extremely Ultraviolet; 13 nm) is underway.
However, it is difficult to develop photoresist resins having high permeability to these wavelengths. Because photoresist used in i-line(365 nm) and KrF(248 nm), wherein its resins consist of aromatic compounds, has high absorbance at the wavelength of 193 nm, the photoresist may not used in 193 nm wavelength. Therefore, photoresist for 193 nm wavelength is developing by using acrylic and alicyclic resins having no aromatic compound. Here, it is difficult to form good patterns because these resins have high absorbance to 193 nm wavelength.
FIG. 1a is a cross sectional view of the vertical pattern formed after development when a coated photoresist composition has low light absorbance. The amount of light reached on the upper portion of a photoresist 12 coated on an underlying layer 10 is approximately equivalent to the lower portion of a photoresist 12. As a result, vertical patterns 14 may be formed. However, when a chemically amplified photoresist is used, sloping patterns 18 is formed since more light exposure is performed on the upper portions of the photoresist 16 relative to the lower portion of the photoresist 16 (See FIG. 1b). In other words, sloping patterns may be formed because concentration gradient of acid generated by exposure is different according to the height in a vertical direction.
Although most studies have placed importance on developing resins having low absorbance to light source, this resin development has reached the limits when light sources such as VUV(157 nm) or EUV(13 nm) are used.